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Class D - heaven or hell ? - Page 2

post #16 of 133
Quote:
Originally Posted by Currawong View Post

Not to entirely trash your reasoning Dave, but do you realise that square waves don't occur in analogue signals at all?  I think though that Class D amps appear to suffer the same problems that digital does in general being that they essentially digitise the sound first to amplify it.

 

Jon Atkinson described the Bel Canto as "unhappy" when dealing with high frequencies, particularly with lower impedance loads. A well designed Class A or Class A/B amp is unlikely to rise past 0.05% THD when driving a 2Ohm load at 20kHz. The REF1000 is closer to 0.5%. Regardless, I'm not the type of person who's obsessed with metered measurements. The Class D sound for me has always been unrefined treble that's dark and grainy, with a lack of air around cymbals and other HF instruments. There's something "off" about it. If little 20lb 1000W amplifiers were a free lunch, everybody would be making them. Who would buy a 150lb. space heater? You'd have to be insane. They are not a free lunch, and that hasn't happened.

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post #17 of 133
Quote:
Originally Posted by DaveBSC View Post

Jon Atkinson described the Bel Canto as "unhappy" when dealing with high frequencies, particularly with lower impedance loads. A well designed Class A or Class A/B amp is unlikely to rise past 0.05% THD when driving a 2Ohm load at 20kHz. The REF1000 is closer to 0.5%. Regardless, I'm not the type of person who's obsessed with metered measurements. The Class D sound for me has always been unrefined treble that's dark and grainy, with a lack of air around cymbals and other HF instruments. There's something "off" about it. If little 20lb 1000W amplifiers were a free lunch, everybody would be making them. Who would buy a 150lb. space heater? You'd have to be insane. They are not a free lunch, and that hasn't happened.

 

From your description, you flat out just don't like the sound signature, so your position on why you don't like Class D/T is justified.

 

From my perspective, it brings me back to the question of, "When is good good enough?"  Sure, I did eventually replace my small, lightweight, efficient, cool-to-the-touch even after hours of listening Class T amplifier with a 62-pound Class A space heater, but in retrospect, the old amp wasn't bad at all. The behemoth definitely sounds amazing, but I can honestly say the Virtue represented amazing value amplification for the money it cost me.

post #18 of 133
Quote:
Originally Posted by Sam Lord View Post

 But the best can amps would see no benefit, IMO, they already get 120+dB S/N + THD/IMD, no?

I suspect you are being ironic, but I'd like to see measurements of these can amps if they exist. Looking at some semiconductor datasheets, one might suspect headphone amps with these specs are easily found in the real world, but I don't see them. If you are being serious, please link some measurements of these amps, I'm very interested.


Edited by thune - 5/14/12 at 8:49pm
post #19 of 133
Quote:
Originally Posted by Currawong View Post
I think though that Class D amps appear to suffer the same problems that digital does in general being that they essentially digitise the sound first to amplify it.

 

No, the signal's not digitized in Class D.

 

With digital, the signal is both sampled and quantized. In Class D, while the signal is effectively sampled, it's not quantized. Signal amplitudes may assume any level. So in that respect Class D is analogue.

 

That said, Class D has never floated my boat. It's only reason for being is high efficiency and small size (which largely comes from its high efficiency). So if high efficiency and/or small size is the main objective, then there's nothing that quite beats Class D. Most all of the work done on Class D since its inception has been to simply bring it up to the levels of performance available from even rather mediocre linear amplifiers.

 

Instead of using a high efficiency amplifier in order to get enough power in a reasonably small space to sufficiently drive an inefficient speaker, I prefer to put the efficiency into the speaker and relax the power requirements from the start regardless of the class of operation. Doubling the loudspeakers sensitivity reduces the power demands by one fourth.

 

Let's say you're able to get sufficient output from your 86dB sensitive speakers (which is about the average sensitivity of loudspeakers out there these days) with a 100 watt amplifier. A speaker with 92dB sensitivity will then only require a quarter of that, or 25 watts. And at 98dB sensitivity, a quarter of that, or just 6.25 watts. And if you want to kick it up another notch with some 104dB sensitive Klipschorns, just 1.6 watts. I mean, even if you're talking about a Class D amplifier with an efficiency in the high 90's, you're still having to burn AT LEAST 100 watts into those 86dB sensitive speakers. Whereas with 98dB sensitivity speakers and a 50% efficient class A amplifier, you're only talking about 13 watts.

 

se


Edited by Steve Eddy - 5/14/12 at 9:48pm
post #20 of 133
Quote:
Originally Posted by Steve Eddy View Post

Instead of using a high efficiency amplifier in order to get enough power in a reasonably small space to sufficiently drive an inefficient speaker, I prefer to put the efficiency into the speaker and relax the power requirements from the start regardless of the class of operation.

This is a beautiful thing. I like having my cake and eating it.
post #21 of 133
Quote:
Originally Posted by Steve Eddy View Post

Instead of using a high efficiency amplifier in order to get enough power in a reasonably small space to sufficiently drive an inefficient speaker, I prefer to put the efficiency into the speaker and relax the power requirements from the start regardless of the class of operation. Doubling the loudspeakers sensitivity reduces the power demands by one fourth.

 

Let's say you're able to get sufficient output from your 86dB sensitive speakers (which is about the average sensitivity of loudspeakers out there these days) with a 100 watt amplifier. A speaker with 92dB sensitivity will then only require a quarter of that, or 25 watts. And at 98dB sensitivity, a quarter of that, or just 6.25 watts. And if you want to kick it up another notch with some 104dB sensitive Klipschorns, just 1.6 watts. I mean, even if you're talking about a Class D amplifier with an efficiency in the high 90's, you're still having to burn AT LEAST 100 watts into those 86dB sensitive speakers. Whereas with 98dB sensitivity speakers and a 50% efficient class A amplifier, you're only talking about 13 watts.

 

se

 

There's definitely a good argument for going that route, as it also allows you to experiment with other flavors like 10 watt SET amps that would be unusable with typical speakers. There are trade offs there to though, increasing driver sensitivity isn't a free lunch either.

post #22 of 133
Quote:
Originally Posted by obobskivich View Post


This is a beautiful thing. I like having my cake and eating it.

 

I like having my mocha and drinking it. biggrin.gif

 

se

post #23 of 133
Quote:
Originally Posted by DaveBSC View Post

 

There's definitely a good argument for going that route, as it also allows you to experiment with other flavors like 10 watt SET amps that would be unusable with typical speakers. There are trade offs there to though, increasing driver sensitivity isn't a free lunch either.

 

Oh certainly. And generally speaking, it's rather more difficult to design a really good quality high efficiency speaker system than a low efficiency speaker system. And for me, there's just a certain uh... I dunno, immediacy and presence to a good high efficiency system that I find particularly attractive and I can listen past a lot of faults even with a high efficiency system that's not up to the best.

 

se

post #24 of 133

I will go one further and post the heresy that if you want to get the best reproduction high efficiency speakers are a must. On the speaker end, not just the electronics. My big bi-amped four ways are 98dB on top, 95 dB on the eighteen inch woofer. My Full Range augmented, about 100dB. All the super dooper high end speakers I have heard sound less coherent or muffled in comparison.

 

I'm not going to argue the point, but after fifty plus years of having at this stereo thing, I find this approach to be the best sounding and most satisfying I have encountered. I wouldn't trade my speaker rigs for anything I have even read about, let alone heard.

 

Headphones? The Stax Omega series are pretty efficient. I have to wonder if the power hungry planars will ever catch up. Some of the same forces are at work. Lighter, more efficient diaphragms yielding greater detail and coherence. Not to mention speed.

 

PS Something not frequently discussed by speaker users is distortion. JBL, a company that gets little discussion on most high end audio forums, has always worked to reduce distortion in transducers. A few years ago they managed to develop a series of large cone speakers that had distortion specs similar to amplifiers. This would not have been possible without embracing high efficiency. Not even remotely possible.
 


Edited by Clarkmc2 - 5/14/12 at 11:12pm
post #25 of 133
Thread Starter 

Interesting - I've been looking at bookshelves in the 1-2K range (not high end, but work with me here) and I'm stunned by the number that are 4 or 6-ohm and less than 85dB. There seems to be an implicit assumption among the big speaker manufacturers - particularly the Brits like KEF - that anyone coming in at that level will be using an SS integrated with at least 60W on tap. I go to Steve Deckert's site and he tells me that his 25W amps will power 'virtually any speaker' and his 2W base model will handle anything around 95dB or above, I know he makes speakers, and Centrance do the same for their elecfronics, but those speakers dont seem to be terribly thick on the ground elsewhere. I've said  it before, but it makes a good case for active speakers on the desktop. 

post #26 of 133
Quote:
Originally Posted by estreeter View Post

Interesting - I've been looking at bookshelves in the 1-2K range (not high end, but work with me here) and I'm stunned by the number that are 4 or 6-ohm and less than 85dB. There seems to be an implicit assumption among the big speaker manufacturers - particularly the Brits like KEF - that anyone coming in at that level will be using an SS integrated with at least 60W on tap. I go to Steve Deckert's site and he tells me that his 25W amps will power 'virtually any speaker' and his 2W base model will handle anything around 95dB or above, I know he makes speakers, and Centrance do the same for their elecfronics, but those speakers dont seem to be terribly thick on the ground elsewhere. I've said  it before, but it makes a good case for active speakers on the desktop. 

 

The market wants small two-way monitors that can extend below 50Hz, and they have to be reasonably affordable. Amplifier power isn't a problem, that's why the speakers are built that way.

post #27 of 133

The problem delivering a good high efficiency speaker is fashion, really. They naturally gravitate to large floorstanding designs, very out of fashion. The design process is a long one, uncommercially long unless your company has been working on the problems for a long, long time. Or unless someone with a very good ear and a good musician to boot is willing to spend five years on the quest. Also not a fashionable way to do business.

 

JBL is an example of the former, getting better at this generation by generation. Unfortunately, high costs and an Asian CEO charged with getting things in line have pretty much killed it off. He offshored everything, and got rid of almost everyone with knowledge of how to make the good stuff.

 

Hammer Dynamics is the subject of the latter model. I brought in my pair for perhaps $1100US. $650 kit, tools, materials for the enclosures, everything. Including a good router and a lot of clamps. Admittedly, the bass was merely very, very good until I applied a Nelson Pass built FirstWatt amp designed especially to drive them to perfection. Then the bass became what we are all looking for. Again, not fashionable. Four feet tall, about fifteen inches square and about a hundred pounds each.


Edited by Clarkmc2 - 5/15/12 at 2:48am
post #28 of 133
Quote:
Originally Posted by Steve Eddy View Post

Quote:
Originally Posted by Currawong View Post
I think though that Class D amps appear to suffer the same problems that digital does in general being that they essentially digitise the sound first to amplify it.

 

No, the signal's not digitized in Class D.

 

With digital, the signal is both sampled and quantized. In Class D, while the signal is effectively sampled, it's not quantized. Signal amplitudes may assume any level. So in that respect Class D is analogue.

 

That said, Class D has never floated my boat. It's only reason for being is high efficiency and small size (which largely comes from its high efficiency). So if high efficiency and/or small size is the main objective, then there's nothing that quite beats Class D. Most all of the work done on Class D since its inception has been to simply bring it up to the levels of performance available from even rather mediocre linear amplifiers.

 

Instead of using a high efficiency amplifier in order to get enough power in a reasonably small space to sufficiently drive an inefficient speaker, I prefer to put the efficiency into the speaker and relax the power requirements from the start regardless of the class of operation. Doubling the loudspeakers sensitivity reduces the power demands by one fourth.

 

Let's say you're able to get sufficient output from your 86dB sensitive speakers (which is about the average sensitivity of loudspeakers out there these days) with a 100 watt amplifier. A speaker with 92dB sensitivity will then only require a quarter of that, or 25 watts. And at 98dB sensitivity, a quarter of that, or just 6.25 watts. And if you want to kick it up another notch with some 104dB sensitive Klipschorns, just 1.6 watts. I mean, even if you're talking about a Class D amplifier with an efficiency in the high 90's, you're still having to burn AT LEAST 100 watts into those 86dB sensitive speakers. Whereas with 98dB sensitivity speakers and a 50% efficient class A amplifier, you're only talking about 13 watts.

 

se

 

Thanks for the clarification. I admit I don't fully understand how Class D works. I'd not thought about efficiency either. This reminds me of some of the arguments for active monitors.

post #29 of 133

  I had the Onkyo class D amp  on audio ayslum regarding class D amps. Wyred for sound has a lineup some like and so do not. The biggest complaints are the bass on most class D amps. I had the Onkyo and the 2150 Outlaw was much better so I bought that one. They run cool and are smaller but I thought the class ab integrated amps were better when I explored them.

post #30 of 133

Here's a nice bookshelf speaker. Doesn't hold a lot of books, but man, what a speaker! biggrin.gif

 

eg-huge8.jpg

 

se

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